Imaging techniques for visualizing coronary heart diseases, in particular for visualizing coronary calcification or stenoses, constitute an important aid in evaluating the condition of the heart. This relates to both preliminary examinations for early diagnosis of circulatory disorders and monitoring a coronary heart disease over a longer period, after a bypass operation or an angioplasty if necessary. Such examinations can improve estimates regarding the risk of a heart attack and can review the success of an intervention or therapy. In particular, non-invasive imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography (PET) are preferably used these days. However, the measurement of cardiac perfusion using PET is very costly and only supplies limited spatial resolution.
Images of the cardiac vessel tree in which vascular restrictions are recognizable can be recorded using coronary CT angiography (CTA) after a contrast agent has been injected. However, even this technique's spatial resolution is still limited due to movement artifacts. Hence, it is no longer possible to make reliable statements about vascular restrictions from such images for volumes below 1 mm3, which occur in the case of vascular restrictions in peripheral coronary artery segments RCA1-4, LM5, LAD6-9 or CX, for example, with lumen cross sections down to 1 mm.
The German patent application with reference number DE 10 2004 055 461.7 furthermore specifies a non-invasive imaging method and an apparatus for visualizing coronary heart diseases, the images of which also make it possible to recognize vascular restrictions or vascular occlusions which previously could not be verified using conventional CTA. The color-coded display of undersupplied or necrotic myocardial areas in a cardiac surface image is also described in this document.
In this case it is problematic that even when a contrast agent is present, the absorption of x-ray radiation in healthy and diseased soft tissue differs only very slightly—approximately 3-5 HU—and this results in large uncertainties when detecting changes in the tissue. Furthermore, these low differences in HU values also require relatively high doses during the examination in order to limit the dose-dependent noise. Although PET allows better differentiation between tissue types than absorption CT, the costs and the radiation exposure of the patient are significantly higher. Furthermore, the spatial resolution of PET examinations is relatively low compared to the resolutions possible in CT.